International patent application WO 96/033010 discloses a disc brake which is preferably operable by way of an electric motor-and a reduction gear. The special features of the prior art brake include that the rotor of the electric motor has an annular design and embraces the reduction gear radially. These provisions achieve that the axial overall length of the actuating unit is greatly shortened. However, the above-mentioned publication does not indicate how defined actuating forces can be generated during operation of the prior art brake.
There is a defined relation between the actuating travel X.sub.Bet, by which the brake pads are pressed against the brake disc, and the actuating force F.sub.Bet generated. This relation can be modeled with sufficient accuracy by a mathematical model, for example, in the way of a static characteristic curve F.sub.Bet (X.sub.Bet). If this relation is known with sufficient accuracy, the actuating or displacement travel which corresponds to a desired actuating force and, in consideration of the gear reduction, the corresponding actuator position can be predetermined (nominal position value) and approached in a positionally controlled manner. This procedure corresponds to a control of the actuating force, i.e., there is an open action sequence (no sensor feedback) with respect to this physical quantity.
On the other hand, it is also possible to reconstruct the current actuating force due to the actuator position which is easily available under measuring technology aspects and is therefore known, by way of a parametric or non-parametric model. However, the clearance position must additionally be known in both cases. The quality of this control, exactly as the reconstruction (calculation) of the actuating force from the position signals of the actuator, depends on the model quality of the process (in this case: the characteristic curve). Because the characteristic curve under review in the operation of the brake is subject to certain significant changes, mainly due to temperature and wear, it is necessary to make an adaptation of this characteristic curve to the current condition of the brake in defined intervals. This adaptation must be effected on the basis of internal signals which are already provided in the electric brake system. This obviates the need for additional external sensor means (no direct measurement of the actuating force). From this results as a demand placed on the mathematical model for the electromechanically operable brake that it describes the behavior under review sufficiently precisely and that the signals used must comprise the desired information on the actuating force.
An object of the present invention is to propose a process and a control system which permit determining the actuating forces that develop during operation. Also, such determination be effected especially without the use of additional sensors.
In terms of process, this object is achieved because a second relation which corresponds to the operation of the brake is determined from the first relation and an information which represents variations of the first relation.
To specify the idea of the present invention, the information representing the variations of the first relation is determined by evaluation of signals which occur during braking operation, in particular, in a displacement travel of a static characteristic curve representing the first relation or in an extension or compression of the static characteristic curve which represents the first relation. The signals preferably represent the position of the actuator and the current value to be sent to the actuator.
In a preferred aspect of the subject matter of the present invention, the speed or the acceleration of the actuator is additionally determined.
Also, it is especially favorable that the second relation is determined according to the formula EQU F.sub.Bet =f(X.sub.Bet)=.lambda.f.multidot..sub.Basis (X.sub.Bet -X.sub.V) (1)
wherein
f.sub.Basis is the first relation, PA1 .lambda. is an extension or compression factor, PA1 X.sub.Bet is the actuating travel of the brake, and PA1 X.sub.V is the displacement travel. PA1 a) a position controller to which the control difference between a nominal actuator position and signals representative of the actual actuator position is sent as an input signal, and connected downstream of which controller is an electronic servo booster having an output signal which actuates the actuator, PA1 b) a characteristic curve adaptation and adaptation monitoring module to which the output signal of the servo booster and the signal representative of the actual actuator position are sent as input quantities, and which furnishes an information about variations of the first relation which occur during operation of the brake, PA1 c) and the information is sent to a performance graph module which calculates actuating travel nominal values from actuating force nominal values in consideration of the variation information, and connected downstream of which module is a conversion module which calculates the signals representative of the nominal actuator position from the actuating travel nominal values. PA1 a) a deceleration controller to which the control difference between signals representative of an actuating force nominal value and an actuating force actual value is sent as an input signal, and connected downstream of which controller is an electronic servo booster having an output signal which actuates the actuator, PA1 b) a characteristic curve adaptation and adaptation monitoring module to which the output signal of the servo booster and the signal representative of the actual actuator position are sent as input quantities, and which furnishes an information about variations of the first relation which occur during operation of the brake, on the one hand, and a signal representative of the actuating travel actual value, on the other hand, which signals PA1 c) are sent to a performance graph module which calculates actuating force actual values from the actuating travel actual values in consideration of the variation information.
In another favorable feature of the present invention, a mathematical model of the brake which comprises the first relation is used wherein the portion of the current being supplied to the actuator, the said portion corresponding to the actuating force, is taken into account to determine both the extension or compression factor and the displacement travel by way of a parameter estimation process.
The established values of the extension or compression factor and of the displacement travel are checked for plausibility preferably before they are employed, and the parameter estimation process is monitored by using the signal representative of the speed of the actuator.
Therefore, the disclosed process of a model-based reconstruction of the actuating force focuses on the modeling of condition-induced variations of the basic characteristic curve (basis characteristic curve) and the methods of determining the adaptation parameters on the basis of internal actuator and brake signals. The latter signals are of major significance and provide the basis of a most accurate metering of the actuating force on the basis of internal actuator signals.
When using the updated static characteristic curve for the metering of the actuating force, principally two procedures are possible which will be reviewed in detail hereinbelow. Preferably, the actuating force as a function of the actuating travel is taken into consideration because in this case it is only necessary to consider the effective rigidity of the entire system and the condition-responsive variations thereof.
A control system according to the present invention for implementing the above-mentioned process distinguishes by the following provisions:
A second variation of the control system for implementing the process of the present invention includes the provision of
The conversion module preferably represents a mathematical model of a gear that acts between the actuator and the brake. Besides, the information about variations of the first relation, which occur during operation of the brake, can be sent to the deceleration controller to update said's parameters.
When the brake is installed in an automotive vehicle it is especially appropriate that an information representative of the rotational speed of the automotive vehicle wheel is sent to the characteristic curve adaptation and adaptation monitoring module.